Light distribution control systems, which are disclosed in Japanese Patent Application Publication No. 2004-161082, are conventionally used to be installed in vehicles.
A light distribution control system disclosed in the Patent Application Publication installed in a vehicle to be controlled is designed to detect values of various parameters associated with physical relationships between the controlled vehicle and either a preceding vehicle or an oncoming vehicle. The “preceding vehicle or oncoming vehicle” will also be referred to as “target vehicle” hereinafter.
The various parameters include the width of the target vehicle, a relative angle between the displayed target vehicle and a reference direction of the controlled vehicle, and a relative distance therebetween. The various parameters also include the speed and a steering position of the controlled vehicle.
According to the detected values of the various parameters, the light distribution control system is designed to individually control the intensity of a beam generated by the headlights of the controlled vehicle and to limit the change of the orientation of the optical axis of each headlight in a vertical direction and a horizontal direction. This aims at preventing the driver of the target vehicle from being dazzled, in other words, from suffering discomfort due to glare.
Such a light distribution control system carries out light-distribution control without quantitatively determining which level of glare the driver of the target vehicle perceives. For this reason, it may unnecessarily limit the change of the orientation of the optical axis of each headlight, and otherwise poorly limit it.
The unnecessary limitation of the change of the orientation of the optical axis of each headlight may cause the visibility of the driver of the controlled vehicle to be more restricted than required.
In addition, the poor limitation of the change of the orientation of the optical axis of each headlight may cause the driver of the target vehicle to become uncomfortable. Note that the controlled vehicle in which such a light distribution control system is installed will be also referred to as “reference vehicle” hereinafter.
From this viewpoint, using, for the light-distribution control, an evaluation value W indicative of the level of glare to be perceived by the driver of the target vehicle has been studied; this evaluation value W is calculated with the use of the following Schmidt-Clausen and Bindels equation [1]:
                    W        =                  5.0          -                      2            ⁢                                                  ⁢            log            ⁢                          ∑                                                E                  Bi                                                                                            C                                              p                        ⁢                                                                                                  ⁢                        00                                                              ⁡                                          [                                              1                        +                                                                                                            L                              u                                                                                      C                              pL                                                                                                                          ]                                                        ⁢                                                            (                                                                        θ                          i                                                ·                        60                                            )                                        0.46                                                                                                          [        1        ]            
where:
EBi represents illumination directed toward the target-vehicle driver's eye from i-th headlamp of the reference vehicle;
θi represents an angle formed by the target-vehicle driver's line of sight and the optical axis of i-th headlamp of the reference vehicle;
Lu represents adaptation luminance of the driver of the target vehicle;
Cp00 represents a constant;
CpL represents a constant; and
i represents an identifier of any one of the headlamps of the headlights
On this Schmidt-Clausen and Bindels equation [1], see J. Mashiko, K. Morita, T. Okada, and M. Sekine, “Analysis of adaptive front-lighting system on glare perceived by oncoming drivers”, in proceedings of 2002 research meetings by National Traffic Safety and Environment Laboratory, pp. 79 to 199.
Specifically, comparison of the evaluation value W with deBoer discomfort rating illustrated in the following table 1 obtains that the driver of the target vehicle would feel discomfort due to glare when the evaluation value W is equal to or lower than the rating of 4.
TABLE 1deBoer Discomfort Rating1Unbearable23Disturbing45Just admissible67Acceptable89Noticeable
For this reason, execution of the light-distribution control to provide the evaluation value W greater than the rating of 4 has been studied.
However, calculation of the evaluation value W requires the values of the various parameters, such as the illumination EBi and the angle θi every time the physical relationships between the reference vehicle and the target vehicle vary.
Particularly, the headlights of the reference vehicle are located on each side of the front end thereof. The headlights are commonly equipped with the first pair of high-beam headlamps and the second pair of low-beam headlamps. The high-beam headlamps are used when the reference vehicle runs on a road where there is no traffic, and the second pair of low-beam headlamps are used when there are target vehicles.
For this reason, calculation of the value of each of the various parameters, such as the illumination EBi and the angle θi, for each of the headlamps is needed. This may take a lot of time and processing load, making it difficult to carry out, in real time, the light-distribution control based on the evaluation value W.